Generally, optical discs and other digital storage media are widely used throughout the world because of their capacity to store and read information. In an optical disc, such as a compact disc (CD), a digital information signal is recorded on one surface and the recorded information is reproduced using a laser beam to pick up the digital signal.
The technology associated with the CD has been expanded to cover other areas such as storing digitized audio, video and alphanumeric information for a variety of purposes, conforming to a number of standards such as digital video disc (DVD), CD-ROM (read only memory), MP3 (Motion Picture Experts Group, Audio Layer 3), etc. (Although reference is generally made to CDs, it is understood that the description and invention generally applies to any optical disc.)
With regard to MP3, the MP3 format for storing and transmitting compressed audio files has made the wide-scale distribution of audio recordings feasible, because a 30 or 40 megabyte digital audio recording of a song can be compressed into a 3 or 4 megabyte MP3 file. Using a typical 56 kbps dial-up connection to the Internet, this MP3 file can be downloaded to a user's computer in a few minutes. Thus, an unauthorized malicious party may read songs from an original and legitimate CD, encode the songs into MP3 format, and place the MP3 encoded song on the Internet for wide-scale illegitimate distribution. Alternatively, the unauthorized malicious party could provide a direct dial-in service for downloading the MP3 encoded song. The illicit copy of the MP3 encoded song can be subsequently rendered by audio playback devices, or can, for example, be decompressed and stored onto a recordable CD for playback on a conventional CD player.
A group by the name of Secured Digital Music Initiative (SDMI) has been established by record companies to protect music companies' copyrights on the Internet by providing disc forgery prevention techniques. SDMI was also founded by the Recording Industry Association of America (RIAA); the initiative has the support of major labels such as Universal, EMI, Sony and Time Warner.
The Secure Digital Music Initiative (SDMI) and others advocate the use of “Digital Watermarks” to identify authorized content material. As in its paper watermark counterpart, a digital watermark is embedded in the content material so as to be detectable, but unobtrusive. An audio playback of a digital music recording containing a watermark, for example, will be substantially indistinguishable from a playback of the same recording without the watermark. A watermark detection device, however, is able to distinguish these two recordings based on the presence or absence of the watermark.
An accurate reproduction of watermarked material will cause the watermark to be reproduced in the copy of the watermarked material. An inaccurate, or lossy reproduction of watermarked material, however, may not provide a reproduction of the watermark in the lossy copy of the material. A number of protection schemes, including those of the SDMI, have taken advantage of this characteristic of lossy reproduction to distinguish legitimate material from illegitimate material, based on the presence or absence of an appropriate watermark. In the SDMI scenario, two types of watermarks are defined: “robust” watermarks, and “fragile” watermarks. A robust watermark is one that is expected to survive a lossy reproduction that is designed to retain a substantial portion of the original content material, such as an MP3 encoding of an audio recording. That is, if the reproduction retains sufficient information to allow a reasonable rendering of the original recording, the robust watermark will also be retained. A fragile watermark, on the other hand, is one that is expected to be corrupted by a lossy reproduction or other illicit tampering.
In the SDMI scheme, the presence of a robust watermark indicates that the content material is copy protected, and the absence or corruption of a corresponding fragile watermark when a robust watermark is present indicates that the copy protected material has been tampered with in some manner. An SDMI compliant device is configured to refuse to render watermarked material with a corrupted or absent fragile watermark, except if the corruption or absence is justified by an “SDMI-certified” process, such as an SDMI compression of copy protected material for use on a portable player. For ease of reference and understanding, the term “render” is used herein to include any processing or transferring of the content material, such as playing, recording, converting, validating, storing, loading and the like.
An SDMI-compliant device has been envisioned that allows an owner of a digital recording, such as a CD, to make only four digital copies, based on detected robust and fragile watermarks, of an original CD per copying session. In addition, the SDMI-compliant device does not allow a copy of the CD to be re-copied, if there is an absence or corruption of a fragile watermark when a robust watermark is present. Further, after the four digital recordings of the original CD (or songs contained thereon) has been met, the SDMI-compliant device will allow a user to copy a section of a track from the original CD of approximately 15 seconds or less. The 15 seconds section of a track may be imported, recorded onto a recordable CD, transmitted over the Internet in the form of an MP3 file, etc.
However, by allowing such a sampling section to be recorded even after the recording limit was reached, the potential for avoiding the 4 song-recording minimum was opened. For example, a song could be imported in 15-second sections, each section individually identified as a separate song or track and including a TOC (Table of Contents). Each section would then be imported and rendered as a sequence of 15 second “songs”, thus piecing together the original song.